The present invention generally relates to ultra-thin photoresist coatings that strongly adhere to underlying substrates. In particular, the present invention relates to increasing the surface roughness of an underlying substrate and applying an ultra-thin photoresist coating over the roughened surface.
As the trend toward smaller and smaller semiconductor device dimensions continues, there is a constant demand to improve the methods of fabricating and processing such devices. For example, improvements in photolithography techniques lead to thinner gates, smaller vias, thinner lines and high density devices among other desirable features. Photolithography techniques can be improved by increasing resolution and increasing critical dimension control. Resolution and critical dimension control are affected by the thickness of a photoresist coating or layer. Therefore, attempts are made to decrease the thickness of photoresist coatings in order to achieve better resolution and critical dimension control.
However, there are limitations associated with making thin photoresist layers. This is because various difficulties are associated with using thin photoresist layers. One difficulty is defect density or the occurrence of pinholes in thin photoresist layers. Another difficulty associated with thin photoresist layers is dewetting. That is, the photoresist layer may pull back from the edge of the wafer or substrate during final spin, dewet around topography (poor step coverage) or lose adhesion in other areas of the wafer. Dewetting thus leads to incomplete or poor pattern formation. Yet another difficulty associated with thin photoresist layers is the inability to provide a uniformly coated substrate. The thinner a photoresist becomes, the ability to uniformly coat a substrate decreases. Photoresists that are not uniformly coated on substrates lead to decreased resolution and loss of critical dimension control.
The present invention provides ultra-thin photoresist coatings that strongly adhere to underlying substrates due to the surface roughness of an underlying substrate. The present invention thus also provides substrates having ultra-thin photoresists, on the order of 500 xc3x85 to 2,000 xc3x85 in thickness, that can be patterned with extremely high resolution enabling the production of thinner gates, smaller vias, thinner trenches, thinner lines, smaller devices and high density devices. The present invention also provides ultra-thin photoresist coatings that uniformly coat underlying substrates.
In one embodiment, the present invention relates to a method of processing a semiconductor substrate, involving the steps of providing the semiconductor substrate having an upper surface; roughening the upper surface of the semiconductor substrate so that the upper surface of the semiconductor substrate has an Rtm of about 10 xc3x85 or more; and depositing an ultra-thin photoresist on the upper surface of the semiconductor substrate, the ultra-thin photoresist having a thickness of about 2,000 xc3x85 or less.
In another embodiment, the present invention relates to a method of increasing adhesion between an ultra-thin photoresist and an upper surface of an underlying substrate, involving the steps of contacting a plasma with the upper surface of the underlying substrate so as to roughen the upper surface; and depositing the ultra-thin photoresist on the roughened upper surface of the underlying substrate, wherein the ultra-thin photoresist has a thickness of about 2,000 xc3x85 or less.
In yet another embodiment, the present invention relates to a method of increasing adhesion between an ultra-thin photoresist and an upper surface of an underlying substrate, involving the steps of contacting an acid solution with the upper surface of the underlying substrate so as to roughen the upper surface, the roughened upper surface of the underlying substrate has an Rtm of about 25 xc3x85 or more; and depositing the ultra-thin photoresist on the roughened upper surface of the underlying substrate, wherein the ultra-thin photoresist has a thickness of about 2,000 xc3x85 or less.